This is moving away from the topic, but flight attendants cannot be flight attendants without their certificate of demonstrated proficiency. If the FA does not follow FAA required safety procedures, which includes enforcing airline-specific procedures that are related to not allowing child seats in seats that are not certified to do so, then they may be subject to a write up by the FAA inspector should they be onboard. They are, however, not expected to fly a plane in case of an emergency.